Herpes simplex virus (HSV) infections are widespread in human populations, and pose a particularly difficult health problem. Genital herpes poses a serious health threat to women, in particular. Pregnant women with active genital herpes infections at the time of delivery have a 50--50 chance of passing it on to their babies. The American Academy of Pediatrics states that 60% of those babies born with HSV infections will die, and half of the survivors will suffer severe damage to the brain, nervous system and eyes ("Pediatrics" 66, 147-9, 1980). It has also been proposed that HSV2 may have a role in the onset of cervical cancer. There has been observed an association between sexual intercourse and cervical cancer, which may be explained by transmission of HSV-2.
Unlike other sexually transmitted diseases such as gonorrhea, syphilis and nongonococcal urethritis, there is currently no cure for herpes infections. Many of the drugs currently in clinical use may not be effective in reducing the severity or the duration of the symptoms. Even after the symptoms disappear, herpes virus tends to remain dormant in nerve tissue, only to be reactivated at a later date to an active phase of infection, causing lesions ("cold sores") and other symptoms to recur. A drug can be considered effective if it diminishes the severity of the lesions, allows for more rapid healing, extends the period between recurrences of herpes infections or stops recurrences altogether.
Herpes simplex virus is one member of the family "Herpetoviridae"; other members of this family which infect humans are varicella-zoster, cytomegalovirus and Epstein-Barr virus. The family also includes various members which attack animals. For example, there are three types of equine herpesvirus, a swine herpesvirus, a canine herpesvirus and a feline herpesvirus, among others.
As with all viruses, herpes virus invades healthy host cells on which it relies to provide its needs for replication. Herpes viruses code for some of the enzymes they need for replication, instead of relying completely on the host cell for all their needs. Hence, herpes viruses are subject to selective inhibition by certain drugs that interfere specifically with viral enzymes.